Do Seedlings Need Light Before They Sprout?
After you’ve planted seeds in a seedling tray, your next move may seem obvious: In addition to warmth, they need light, right? In reality, there are seeds that need darkness to germinate, not light. The time will come when the seeds should be placed in direct sunlight. You may not aspire to become a master gardener, but you can become the master of your own garden when you take the time to learn how to nurture seeds through their fussiest phase of all.
Most seeds germinate best when they’re placed in the dark. The presence of light, which is crucial to seedling development, may actually stunt the process of germination.
Yes, Most Seeds Thrive in Darkness
Fussy may be an understatement, for it’s also easy to forget that seeds are living entities. Underneath that tough coating lies an embryo and food. While your seeds may look viable from the outside, they will sprout only when conditions are right or when they are exposed to the proper temperature and the right amount of air, moisture and light, says Harvest to Table.
Of these life-sustaining elements, light is the differentiator of the group. Put another way, seeds have different light needs, PennState Extension says. As much as it might surprise or shock you, it’s vital to know that most seeds germinate best when they’re placed in the dark. Light may actually stunt the process of germination.
At this point and beyond, it can be helpful to distinguish between the lighting needs of seeds as they burrow in the soil and the light they need once they sprout and become seedlings. All seedlings need sunlight to grow strong. Their “end game,” remember, is to survive fluctuating conditions in the great outdoors. To give your seeds the specific care they need, check the instructions on the seed packet.
Give Your Seeds a Good Soak
Your heart may start beating a little faster once you open the packet and inspect the seeds to ensure they are intact. Toss any seeds that appear damaged, as the seed embryo may be damaged too. Then, if you can harness your enthusiasm and postpone planting the seeds for a day, soak the seeds overnight. This process softens the seed coating and eases germination.
Some seeds respond to this technique better than others. Seeds that enjoy a good soak include:
Place the seeds in a shallow bowl of warm water for at least 12 hours or overnight. If submerging the seeds makes you nervous (though it shouldn’t), you can wrap the seeds in a damp paper towel and then place the towel in a plastic bag. Seal the bag to ensure the seeds absorb as much moisture as possible.
Know the Seeds That Need Light to Germinate
In all likelihood, you will find many similarities among seeds’ needs. To germinate, they usually require the correct number of seeds per cube. For vegetables, this usually means only one or two seeds; for herbs, up to six seeds; and for lettuce and other greens, between six and 12 seeds, Tower Garden says. Seeds also require a burrowing depth that is about three times their thickness; moist, cool and finely textured seedling soil; and an indoor temperature between 60 and 70 degrees Fahrenheit. To prevent overwatering, take a cue from the experts and water the seeds from the bottom rather than from the top, where water can easily pool.
Only some seeds need light to germinate. They include some vegetable seeds, which are usually among the smallest seeds, and lettuce, which also does not need to be covered with soil, though the seeds can tolerate a thin layer. Other seeds also require little soil cover and therefore may germinate in light. These include:
- Brussels sprouts
- Chinese cabbage
No matter what you’re growing, it’s always a good idea to cover the seedling tray with the dome that accompanied it or with plastic wrap. This seal will keep the atmosphere humid and the soil moist until the seedlings sprout.
Seedlings Need Light
Once they sprout, it’s time to shift gears. Your seeds may not have needed light to germinate, but the seedling will. Still, simply placing the tray in a sunny widowsill probably will not produce the steady growth for which you’re looking. In fact, seedlings that grow painfully slowly and then tall and leggy are dead ringers for those that aren’t getting enough light. This is why many experienced gardeners recommend grow lights.
LED or fluorescent lights can be a great solution provided that they’re used properly. At this stage in the growing process, Upstart University says gardeners are most likely to make one of three common mistakes: an insufficient amount of light, lights that are placed too far away from the seedlings or lights that are not left on long enough. Fortunately, these problems are easily remedied. The main fixes involve coverage and the amount of lighting, so place LED bars 8 to 10 inches apart from one another and place fluorescents 4 to 5 inches apart from one another.
The point with coverage is to make sure that the lights cover the entire seedling tray. In terms of the amount of lighting, place LED lights 8 to 12 inches above the top of the seedlings and place fluorescents about 5 to 6 inches above the top of the seedlings. Most seedlings require 14 to 16 hours of light per day. It can be a demanding schedule to accommodate, which is why many gardeners gain the upper hand by hooking up the grow lights to a timer.
Grow Strong Seedlings
Mastering the hugely important issue of light should do wonders for your confidence and your seedlings, but gardening is not a perfect science. Sometimes, after rushing over to check your seedling tray, you may be faced with things you can’t explain. Fortunately, many issues at this stage are still easily remedied.
Take, for example, the sudden presence of overdeveloped or crowded seedlings. This is actually an ideal time to assign one seedling per cube, so thin out the tray now. You should move with equal urgency if you spot leaves that are turning yellow, brown or white or look dull compared to the others, Get Busy Gardening says. Most often, this is a sign of overwatering, so be sure to continue to water your seedlings from the bottom of the tray. You can also get a soil water gauge to keep the soil just right and to prevent mold from growing.
Keep the room temperature at 65 degrees or higher, run an oscillating fan near the seedlings to keep the air moving and to prepare them for the winds they will eventually face when they are moved outdoors and once the seedlings sprout leaves, use an organic fertilizer rather than a chemical fertilizer to reduce the risk of leaf burn. Once you’re ready to transplant your hardy seedlings outdoors, don’t be surprised if you feel like the master of your garden. You know what this means: You’ve seen the light and have gone from being a mere gardener to a master gardener once and for all.
- Harvest to Table: Vegetable Seed Germination Special Requirements
- PennState Extension: Seed and Seedling Biology
- Tower Garden: How to Grow Strong, Healthy Seedlings in 7 Steps
- Upstart University: How to Give Seedlings Enough Light to Be Healthy
- Get Busy Gardening: How To Fix Common Seedling Problems
Mary honed her journalism skills in two of Chicago’s scrappiest newsrooms: The Daily Herald and then the Chicago Sun-Times. She took this knowledge, combined it with her experience in running two marketing communication companies and now writes about communication, marketing, careers and other timely business topics for myriad national publications.
Do Seedlings Need Light Before They Sprout?. Seeds, when they come to us in seed packages, are dormant. For a plant to grow from the seed, that dormancy has to be broken. Some seeds break dormancy when their seeds get wet. Some require that fire or pressure break their husk. Others require light.